FIG. 10 shows an optical module 201 including a transmitting portion 202 and a receiving portion 203 (e.g., reference is made to Patent Document 1). In this optical module 201, the transmitting portion 202 generates a digital optical signal, and this optical signal is outputted to an optical fiber 205. The optical module 201 receives a digital optical signal. This optical signal is reflected by an optical element 204 and the reflected light signal is incident to the light receiving portion 203. This optical module 201 is able to transmit and receive digital optical signals. Patent Document 1: Japanese Patent Application Laid-Open No. 10-93133